Message-ID: <20210715212657.GI22357@magnolia>
Date:   Thu, 15 Jul 2021 14:26:57 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v14 098/138] iomap: Use folio offsets instead of page
 offsets

On Thu, Jul 15, 2021 at 04:36:24AM +0100, Matthew Wilcox (Oracle) wrote:
> Pass a folio around instead of the page, and make sure the offset
> is relative to the start of the folio instead of the start of a page.
> Also use size_t for offset & length to make it clear that these are byte
> counts, and to support >2GB folios in the future.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/iomap/buffered-io.c | 85 ++++++++++++++++++++++--------------------
>  1 file changed, 44 insertions(+), 41 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index fbe4ebc074ce..707a96e36651 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -75,18 +75,18 @@ static void iomap_page_release(struct folio *folio)
>  }
>  
>  /*
> - * Calculate the range inside the page that we actually need to read.
> + * Calculate the range inside the folio that we actually need to read.
>   */
> -static void
> -iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
> -		loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)
> +static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
> +		loff_t *pos, loff_t length, size_t *offp, size_t *lenp)
>  {
> +	struct iomap_page *iop = to_iomap_page(folio);
>  	loff_t orig_pos = *pos;
>  	loff_t isize = i_size_read(inode);
>  	unsigned block_bits = inode->i_blkbits;
>  	unsigned block_size = (1 << block_bits);
> -	unsigned poff = offset_in_page(*pos);
> -	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
> +	size_t poff = offset_in_folio(folio, *pos);
> +	size_t plen = min_t(loff_t, folio_size(folio) - poff, length);

I'm confused about 'size_t poff' here vs. 'unsigned end' later -- why do
we need a 64-bit quantity for poff?  I suppose some day we might want to
have folios larger than 4GB or so, but so far we don't need that large
of a byte offset within a page/folio, right?

Or are you merely moving the codebase towards using size_t for all byte
offsets?

The rest of the conversion code looked ok though.

--D

>  	unsigned first = poff >> block_bits;
>  	unsigned last = (poff + plen - 1) >> block_bits;
>  
> @@ -124,7 +124,7 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
>  	 * page cache for blocks that are entirely outside of i_size.
>  	 */
>  	if (orig_pos <= isize && orig_pos + length > isize) {
> -		unsigned end = offset_in_page(isize - 1) >> block_bits;
> +		unsigned end = offset_in_folio(folio, isize - 1) >> block_bits;
>  
>  		if (first <= end && last > end)
>  			plen -= (last - end) * block_size;
> @@ -134,31 +134,31 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
>  	*lenp = plen;
>  }
>  
> -static void iomap_iop_set_range_uptodate(struct page *page,
> -		struct iomap_page *iop, unsigned off, unsigned len)
> +static void iomap_iop_set_range_uptodate(struct folio *folio,
> +		struct iomap_page *iop, size_t off, size_t len)
>  {
> -	struct inode *inode = page->mapping->host;
> +	struct inode *inode = folio->mapping->host;
>  	unsigned first = off >> inode->i_blkbits;
>  	unsigned last = (off + len - 1) >> inode->i_blkbits;
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&iop->uptodate_lock, flags);
>  	bitmap_set(iop->uptodate, first, last - first + 1);
> -	if (bitmap_full(iop->uptodate, i_blocks_per_page(inode, page)))
> -		SetPageUptodate(page);
> +	if (bitmap_full(iop->uptodate, i_blocks_per_folio(inode, folio)))
> +		folio_mark_uptodate(folio);
>  	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
>  }
>  
> -static void iomap_set_range_uptodate(struct page *page,
> -		struct iomap_page *iop, unsigned off, unsigned len)
> +static void iomap_set_range_uptodate(struct folio *folio,
> +		struct iomap_page *iop, size_t off, size_t len)
>  {
> -	if (PageError(page))
> +	if (folio_test_error(folio))
>  		return;
>  
>  	if (iop)
> -		iomap_iop_set_range_uptodate(page, iop, off, len);
> +		iomap_iop_set_range_uptodate(folio, iop, off, len);
>  	else
> -		SetPageUptodate(page);
> +		folio_mark_uptodate(folio);
>  }
>  
>  static void
> @@ -169,15 +169,17 @@ iomap_read_page_end_io(struct bio_vec *bvec, int error)
>  	struct iomap_page *iop = to_iomap_page(folio);
>  
>  	if (unlikely(error)) {
> -		ClearPageUptodate(page);
> -		SetPageError(page);
> +		folio_clear_uptodate(folio);
> +		folio_set_error(folio);
>  	} else {
> -		iomap_set_range_uptodate(page, iop, bvec->bv_offset,
> -						bvec->bv_len);
> +		size_t off = (page - &folio->page) * PAGE_SIZE +
> +				bvec->bv_offset;
> +
> +		iomap_set_range_uptodate(folio, iop, off, bvec->bv_len);
>  	}
>  
>  	if (!iop || atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending))
> -		unlock_page(page);
> +		folio_unlock(folio);
>  }
>  
>  static void
> @@ -237,7 +239,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  	struct iomap_page *iop = iomap_page_create(inode, folio);
>  	bool same_page = false, is_contig = false;
>  	loff_t orig_pos = pos;
> -	unsigned poff, plen;
> +	size_t poff, plen;
>  	sector_t sector;
>  
>  	if (iomap->type == IOMAP_INLINE) {
> @@ -246,14 +248,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  		return PAGE_SIZE;
>  	}
>  
> -	/* zero post-eof blocks as the page may be mapped */
> -	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
> +	/* zero post-eof blocks as the folio may be mapped */
> +	iomap_adjust_read_range(inode, folio, &pos, length, &poff, &plen);
>  	if (plen == 0)
>  		goto done;
>  
>  	if (iomap_block_needs_zeroing(inode, iomap, pos)) {
> -		zero_user(page, poff, plen);
> -		iomap_set_range_uptodate(page, iop, poff, plen);
> +		zero_user(&folio->page, poff, plen);
> +		iomap_set_range_uptodate(folio, iop, poff, plen);
>  		goto done;
>  	}
>  
> @@ -264,7 +266,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  	/* Try to merge into a previous segment if we can */
>  	sector = iomap_sector(iomap, pos);
>  	if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
> -		if (__bio_try_merge_page(ctx->bio, page, plen, poff,
> +		if (__bio_try_merge_page(ctx->bio, &folio->page, plen, poff,
>  				&same_page))
>  			goto done;
>  		is_contig = true;
> @@ -296,7 +298,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  		ctx->bio->bi_end_io = iomap_read_end_io;
>  	}
>  
> -	bio_add_page(ctx->bio, page, plen, poff);
> +	bio_add_folio(ctx->bio, folio, plen, poff);
>  done:
>  	/*
>  	 * Move the caller beyond our range so that it keeps making progress.
> @@ -531,9 +533,8 @@ iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
>  		truncate_pagecache_range(inode, max(pos, i_size), pos + len);
>  }
>  
> -static int
> -iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff,
> -		unsigned plen, struct iomap *iomap)
> +static int iomap_read_folio_sync(loff_t block_start, struct folio *folio,
> +		size_t poff, size_t plen, struct iomap *iomap)
>  {
>  	struct bio_vec bvec;
>  	struct bio bio;
> @@ -542,7 +543,7 @@ iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff,
>  	bio.bi_opf = REQ_OP_READ;
>  	bio.bi_iter.bi_sector = iomap_sector(iomap, block_start);
>  	bio_set_dev(&bio, iomap->bdev);
> -	__bio_add_page(&bio, page, plen, poff);
> +	bio_add_folio(&bio, folio, plen, poff);
>  	return submit_bio_wait(&bio);
>  }
>  
> @@ -555,14 +556,15 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
>  	loff_t block_size = i_blocksize(inode);
>  	loff_t block_start = round_down(pos, block_size);
>  	loff_t block_end = round_up(pos + len, block_size);
> -	unsigned from = offset_in_page(pos), to = from + len, poff, plen;
> +	size_t from = offset_in_folio(folio, pos), to = from + len;
> +	size_t poff, plen;
>  
> -	if (PageUptodate(page))
> +	if (folio_test_uptodate(folio))
>  		return 0;
> -	ClearPageError(page);
> +	folio_clear_error(folio);
>  
>  	do {
> -		iomap_adjust_read_range(inode, iop, &block_start,
> +		iomap_adjust_read_range(inode, folio, &block_start,
>  				block_end - block_start, &poff, &plen);
>  		if (plen == 0)
>  			break;
> @@ -575,14 +577,15 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
>  		if (iomap_block_needs_zeroing(inode, srcmap, block_start)) {
>  			if (WARN_ON_ONCE(flags & IOMAP_WRITE_F_UNSHARE))
>  				return -EIO;
> -			zero_user_segments(page, poff, from, to, poff + plen);
> +			zero_user_segments(&folio->page, poff, from, to,
> +						poff + plen);
>  		} else {
> -			int status = iomap_read_page_sync(block_start, page,
> +			int status = iomap_read_folio_sync(block_start, folio,
>  					poff, plen, srcmap);
>  			if (status)
>  				return status;
>  		}
> -		iomap_set_range_uptodate(page, iop, poff, plen);
> +		iomap_set_range_uptodate(folio, iop, poff, plen);
>  	} while ((block_start += plen) < block_end);
>  
>  	return 0;
> @@ -661,7 +664,7 @@ static size_t __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
>  	 */
>  	if (unlikely(copied < len && !PageUptodate(page)))
>  		return 0;
> -	iomap_set_range_uptodate(page, iop, offset_in_page(pos), len);
> +	iomap_set_range_uptodate(folio, iop, offset_in_folio(folio, pos), len);
>  	__set_page_dirty_nobuffers(page);
>  	return copied;
>  }
> -- 
> 2.30.2
> 

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